This invention relates to an abnormal voltage protection device such as an arrestor for instantaneous protection of an electric circuit against any abnormal voltage.
Three-phase abnormal voltage protection devices of conventional construction comprise a metallic housing having a circular cross section connected to ground, and three stacks of non-linear resistors disposed at equal angular intervals equidistant from the longitudinal axis of the housing and adapted to be connected to the three-phases of an associated electric source respectively. For low AC voltages, the non-linear resistors function as a substantially perfect capacitor and has problems. It has been proven by theoretical analysis that due to stray capacitances developed between the resistor stacks and between each resistor stack and the metallic housing the non-linear resistors of each stack share unevenly the AC voltage applied across the stack. That is, that portion of the stack near to the high voltage side is in an overvoltage state resulting in electrical deterioration. Also upon the occurrence of a line to ground fault, the high voltage portions of the stacks for the sound phases have their voltage share greatly increased. Thus the non-linear resistors disposed in the high voltage portions of the stacks are subject to rapid deterioration.
Accordingly it is an object of the present invention to provide a new and improved three-phase abnormal voltage protection device including three stacks of non-linear reactors, one for each phase, wherein the voltage applied across each stack is uniformly divided among the non-linear resistors of each stack including those forming the high voltage portion thereof while the inter-phase effects is decreased to prevent the deterioration of the non-linear resistors and improve the performance.